Vibration dampening for long twisted turbine blades

ABSTRACT

Lashing long twisted turbine blades in groups with a small Vshaped gap between the groups, which tends to close due to the untwisting of the blades, when they are subjected to high centrifugal forces, provides a substantially continuous lashing ring with good vibration dampening characteristics, which is sufficiently flexible to allow for thermal expansion and contraction, and cooperates with the vibration reducing characteristic of joining the blades into groups to minimize stress vibrations in such blades.

United States Patent [191 Trumpler, Jr.

[ VIBRATION DAMPENING FOR LONG TWISTED TURBINE BLADES [75] Inventor: William E. Trumpler, Jr.,

Philadelphia, Pa.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: Aug. 9, 1971 [21] Appl. No.: 169,979

52 us. Cl. 416/196 51 int. Cl. Fold 5/10 58 Field of Search 416/189-196 [56] I References Cited UNITED STATES PATENTS 1,304,793 5/1919 Moore 416/191 1,639,247 8/1927 Zoelly et al.... 416/190 2,283,901 5/1942 Arnold l 416/191 2,391,623 12/1945 Heppner.... 416/191 2,510,734 6/1950 Bodger 416/190 1 Mar. 5, 1974 3,572,970 3/1971 Smuland 416/190 UX 3,588,278 6/1971 Ortolano 416/190 FOREIGN PATENTS OR APPLICATIONS 69,842 9/1958 France 416/196 Primary ExaminerEverette A. Powell, Jr Attorney, Agent, or FirmF. J Baehr, Jr.

[5 7] ABSTRACT Lashing long twisted turbine blades in groups with a small V-shaped gap between the groups, which tends to close due to the untwisting of the blades, when, they are subjected to high centrifugal forces, provides a substantially continuous lashing ring with good vibration dampening characteristics, which is sufficiently flexible to allow for thermal expansion and contraction, and cooperates with the vibration reducing characteristic of joining the blades into groups to minimize stress vibrations in such blades.

4 Claims, 3 Drawing Figures PATENTED 5 74 SHEU 2 0F 2 WW U0 LL FF FIG. 3

VIBRATION DAMPENING FOR LONG TWISTED TURBINE BLADES BACKGROUND OF THE INVENTION This invention relates to turbine blades and more particularly to lashing long twisted turbine blades in groups.

The large volumetric flow of steam encountered in the exhaust of large steam turbines used in present day power generating stations requires blades having alarge' open area resulting in long blades disposed on a large diameter rotor. Such blades generally have an air foil cross section, which changes its shape and angle as the blades extend radially outwardly due to the change in linear speed of the blade from its root to its tip. These twisted blades tend to untwist as the rotor spins at high speeds and this twisting action can be utilized to provide vibration dampening as shown in US. Pat. No. 2,510,734.

SUMMARY OF THE INVENTION In general, an annular array of circumferentially spaced twisted blades fastened to a rotor, when made in accordance with this invention, are joined together in groups by a segmented ring with a small gap between adjacent groups of blades. The gap is of such configuration that only a small portion thereof closes as the blades are rotated and tend to untwist as a group, thereby providing a substantially continuous ring, which cooperates with the blade grouping to reduce vibration and to still allow for thermal expansion and elastic deformation of the rotor.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings in detail, FIG. ll shows a segment of an annular array of circumferentially spaced rotatable blades l for a steam turbine (not shown), wherein the blades 1 have a general air foil cross section, which changes shape and angle from its root 3 to its tip 5. The air foil generally has a rounded leading edge 7 and a sharper trailing edge 9. The blades are fastened to a rotor 11 and extend out radially therefrom.

Lashing rings 13 and 15 are disposed adjacent the tip end of the blades 1 and are concentric with the axis of the rotor ll. The lashing rings 13 and are segments of a circular ring and are made integral with or are welded to each blade. The lashing segments join the blades in groups having three or more blades therein. The number of blades in a group depending on the resonant frequency of the array of blades and the speed of the rotor. The groups are separated by a small jagged gap 117 in the lashing rings 13 and 115..

As shown in FIG. 2, the gaps 117 are generally V- shaped and the V generally opens in the direction of rotation of the blades. The lashing rings E3 and 15 generally have an oval cross section with the major axis aligned with the axis of the rotor H1 so that the leading and trailing edges or margins I19 and M respectively are rounded edges to minimize resistance to steam flow.

Downstream legs 23 of the V-shaped gap are generally shorter than upstream legs 25 thereof, so that as the blades tend to untwist due to the centrifugal forces induced by rotating them, the group of blades tend to rotate clockwise as shown in FIG. 2 causing the short legs of the V-shaped gap to close. As the gap closes it provides a substantially continuous interlocking ring that results in snubbing and vibration dampening, which cooperates with the blade grouping, to minimize vibration of the blades and yet provides sufficient flexibility to allow for thermal expansion and contraction of the rotor. Joining the blades in groups is a particularly advantageous arrangement for reducing vibration at resonant speeds, as described in the Ft. 1. Ortolano et al., US. Pat. No. 3,588,278, issued June 28, 1971, and assigned to the same assignee, while the snubbing or dampening caused by the gap closing will absorb any type of vibration energy, thus minimizing the vibration stresses in the rotating blades.

FIG. 3 shows a modification, in which the gaps 17' generally extend across the lashing rings 13 and and intercept the margins H9 and Zll on a plane extending from the leading edge of one blade to the trailing edge of an adjacent blade. The gaps generally have a loop 27 disposed generally in the center of the gap and the loop opens in the direction of rotation.

The loop is generally formed by drilling a hole through the lashing ring at the center of the gap and placing a disk like plug 29 in the hole and then welding the plug 29 to the lashing ring on one side of the hole. The hole is sized to provide the loop shaped portion of the gap. A tongue and groove arrangement could also be utilized.

Due to the centrifugal force caused by the spinning rotor the groups of blades tend to untwist causing each group to rotate in the clockwise direction as shown in FIG. 3. This causes one side of the loop shaped gap to close forming a substantially continuous interlocking ring to provide vibration dampening and snubbing and yet still provide sufficient flexibility in the array of blades to allow for thermal expansion and contraction of the rotor llll, thus minimizing vibration induced stresses in the blades. Being formed as an integral portion of the lashing or shroud ring this type of damper will not jeopardize other accepted design features of strength and tuning of the blade groups as it wears.

While the drawings show two lashing rings, a single lashing ring, a shroud ring and a shroud ring and lashing ring could be advantageously made in accordance with this invention to produce the desired vibration reducing characteristics hereinbefore described.

What is claimed is:

ll. An annular array of circumferentially spaced twisted blades fastened to a rotor, said blades being joined together into integral groups by a segmented ring which is integral with a plurality of blades, and which is generally of uniform cross section in each group, there being a small gap between adjacent segments of said ring, said gap being generally V-shaped, the V generally opening in the direction of the rotation of the blade, the V having legs which extend to the rings margins, and the downstream leg of the V being shorter than an upstream leg thereof, so that only a small portion thereof adjacent one side thereof closes as the blades are rotated and tend to untwist as a group, thereby providing a substantially continuous interlocking segmented ring, which cooperates with the blade grouping to reduce vibration and to allow for thermal expansion and elastic deformation of said rotor.

wherein the ring is disposed adjacent the outer periphcry of the annular array of blades and each group has at least three blades therein. 

1. An annular array of circumferentially spaced twisted blades fastened to a rotor, said blades being joined together into integral groups by a segmented ring which is integral with a plurality of blades, and which is generally of uniform cross section in each group, there being a small gap between adjacent segments of said ring, said gap being generally V-shaped, the V generally opening in the direction of the rotation of the blade, the V having legs which extend to the ring''s margins, and the downstream leg of the V being shorter than an upstream leg thereof, so that only a small portion thereof adjacent one side thereof closes as the blades are rotated and tend to untwist as a group, thereby providing A substantially continuous interlocking segmented ring, which cooperates with the blade grouping to reduce vibration and to allow for thermal expansion and elastic deformation of said rotor.
 2. An annular array of blades as set forth in claim 1, wherein the blades are joined in groups by concentric segmented rings with a small gap in each ring between adjacent groups of blades.
 3. An annular array of blades as set forth in claim 2, wherein the rings are lashing rings.
 4. An annular array of blades as set forth in claim 1, wherein the ring is disposed adjacent the outer periphery of the annular array of blades and each group has at least three blades therein. 